Function Recognises Variable Without Arguments Or Global Variable Calling.

[bowlofred]

1) does python search for global value (and use them) by default if local not found? (or does it only do this if the input args are empty?

The first. It will use a variable from a larger scope (such as global) if there isn't a local binding variable. The follow-on is that there is no local binding variable if it is not assigned (written to) within the function.

Compare:

a = 10

def function():
    print(a)

function()

and

a = 10

def function():
    print(a)
    a = 1

function()

Because a is assigned at some point in the second function, it is a local variable.

2) why if you use a while loop like below, do I get the error of not finding the global variable, but don't get that error for finding a,b etc.?

Because a and b were never assigned in the function, but is_true is assigned within.

From Python Docs

If a name binding operation occurs anywhere within a code block, all uses of the name within the block are treated as references to the current block. This can lead to errors when a name is used within a block before it is bound. This rule is subtle. Python lacks declarations and allows name binding operations to occur anywhere within a code block. The local variables of a code block can be determined by scanning the entire text of the block for name binding operations.

The global and nonlocal statements can override this behavior.